石榴子石热红外波谱特征研究

Thermal-Infrared Spectroscopy of Garnet Minerals

近年来短波红外高光谱技术已成功应用于含水含羟基蚀变矿物及矿床学研究,但是对于不含水不含羟基矿物探测效果不好,而热红外高光谱技术可以弥补这一技术缺陷,对于含Si_(n)O_(k),SO_(4),CO_(3)和PO_(4)等原子基团的矿物具有良好的应用前景。石榴子石是一种重要的含Si_(n)O_(k)基团的岛状结构硅酸盐矿物,根据成分可分为钙铝榴石、钙铁榴石、镁铝榴石、铁铝榴石及锰铝榴石等不同端元,石榴子石成分对成矿温压环境及成矿中心预测具有重要的研究意义。目前针对石榴子石热红外波谱特征研究非常欠缺。故采集不同成分、不同颜色石榴子石样品16件,创新性地运用美国Agilent4300热红外波谱仪开展热红外波谱特征研究,同时运用美国Niton手持式XRF分析仪开展石榴子石同一测量位置的SiO_(2),MgO,Al_(2)O_(3),K_(2)O,CaO和Fe_(2)O_(3)等主量元素含量测试,并分析波谱吸收位置与主量元素含量之间的关系。结果表明石榴子石在热红外波段10~13μm具有左高右低的双峰式诊断性波谱特征,在11.5μm附近呈现一个主吸收谷,在12μm附近有一个次级吸收谷,且主吸收谷及次级吸收谷波长位置与石榴子石Al_(2)O_(3)和Fe_(2)O_(3)含量具有良好的相关性,相关系数大于0.9,即波谱吸收谷的波长位置与Al_(2)O_(3)含量具有线性负相关关系,与Fe_(2)O_(3)含量具有线性正相关关系。据此研究结果,可以快速开展石榴子石矿物成分的野外鉴定,还可以快速开展矽卡岩矿床野外蚀变分带研究,进而指导找矿勘查。揭示了不同成分石榴子石矿物的热红外波谱特征,对其他架状硅酸盐、岛状硅酸盐、单链状硅酸盐、碳酸盐、硫酸盐矿物的热红外波谱特征研究具有重要的指导意义。

Hyperspectral technology is a new non-damaging method for mineral detection and identification.In recent years,short-wave infrared(SWIR)technology with a wavelength of 1.1~2.5μm had been successfully applied in alteration minerals and correlated ore deposits studies.However,SWIR technology was more suitable for hydrated and hydroxyl-bearing minerals,and was not sensitive for minerals containing Si_(n)O_(k),SO_(4),CO_(3),PO_(4).Then thermal-infrared technology with the wavelength of 3~14μm could remedy the technical defect,and was more detectable for minerals without hydro and hydroxyl.Garnet is an important neosilicate mineral containing Si_(n)O_(k),divided into many groups according to the chemical components including grossular,andradite,pyrope,almandine,spessartine et al.,and garnet is indicative for temperature,pressure and other mineral forming conditions and ore prospecting.Recently,little research on thermal-infrared spectroscopy of garnet minerals has been conducted.In this paper,sixteen garnet minerals with different components and colors were collected,and thermal-infrared spectroscopy of these garnet minerals was firstly studied using Agilent 4300 thermal-infrared spectrometer.What’s more,the content of principal elements including SiO_(2),MgO,Al_(2)O_(3),K_(2)O,CaO,Fe_(2)O_(3)of these garnet minerals was measured using Niton XRF analyzer at the same position,and the relationship between the content of principal elements and absorption wavelength were analyzed.The result indicated that garnet minerals had diagnostic features with twin peaks in the thermal-infrared band region of 10~13μm,which presented the main absorption at about 11.5μm and a secondary absorption at about 12μm.The wavelength at these two absorption was well correlated with the Al_(2)O_(3)and Fe_(2)O_(3)content of garnet minerals,which was linear negative correlated with the content of Al_(2)O_(3),and was linear positive correlated with the content of Fe_(2)O_(3).The results can help quickly identify the chemical components of garnet minerals and add alteration zoning of skarn ore deposits in the field that indicate ore prospecting.The study started an application of Agilent4300 thermal-infrared spectrometer in the mineral study and gave a good example of thermal-infrared spectroscopy of garnet minerals study,which could provide the fundamental basis for thermal-infrared spectroscopy of other tectosilicates,neosilicates,single-chain silicates,carbonates and sulphates.